Bitcoin is banned by government because, government feel threaten and they don't have control over bitcoin, government feel bitcoin is illegal because it not a register company, no tax, so they feel is illegal, and banned it.
Few demerits which govt or the organized body consider is that : -
1) It can be misused easily and it can cause a national threat .
2) Black money can be easily rotated and deposited anywhere in the world through this means.
3) Its is traceable but not fully in direct control of the govt like how banks accounts are.
4) Misappropriate in the taxes can happen through this form.
It is not actually banned they are just saying it in the social media that it should not be tolerated, they are just giving restrictions about it.
And they don't want the idea in bitcoin as they kept saying that they are just manipulating the price of bitcoin and are just scamming people and in the end they will all get the funds of it.